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Earth Science: Ch 14 Review:

Ch 14 Review

The

Vast

World

Ocean

The Vast World Ocean: Review

The World’s Oceans:


Nearly
71%

of the Earth’s surface is
covered by ocean.



Oceanography
,

the study of the world’s
oceans, is a science that draws on the
methods and knowledge of geology,
chemistry, physics, and biology to study all
aspects of the world’s oceans.



The world’s oceans can be divided into 4
main
ocean basins
:


The Pacific Ocean


the Atlantic Ocean



the Indian ocean



the Arctic ocean.




The Vast World Ocean: Review

The World’s Oceans:


The
Pacific Ocean
is the largest of Earth’s
oceans.
It is the single largest
geographical feature on the Earth’s
surface.



It covers more than half the ocean
surface on Earth.
It is also the world’s
deepest ocean with an average depth of
3940 meters.



The
Atlantic Ocean
is about half the size
of the Pacific Ocean.
It is a relatively
narrow ocean compared to the Pacific.
Both the Atlantic and Pacific are bounded
to the east and west by continents.





The Vast World Ocean: Review

The World’s Oceans:


The
Indian Ocean
is slightly smaller than
the Atlantic Ocean, but is about the same
average depth.





The
Arctic Ocean
is about 7% of the size
of the pacific ocean.
It is only a little
more than one quarter as deep as the rest
of the oceans.








The Vast World Ocean: Review

The World’s Oceans:



The topography of the ocean floor is as
diverse as that of the continents.



Bathymetry

is the measurement of ocean
depths and the charting of the shape or
topography of the ocean floor.



In the 1920’s, a technological
breakthrough occurred with the invention
of
sonar
, a type of depth sounding
equipment.
Sonar is an acronym for
S
ound
N
avigation
A
nd
R
anging.












The Vast World Ocean: Review

The World’s Oceans:



In the last few decades, more complex
systems using
multi
-
beam sonar systems
have developed.



Measuring the shape of the ocean floor
from space with
satellites

is another
recent technological breakthrough that
has led to a better understanding.



Another way scientists learn about the
ocean floor is by direct contact; going
there in small
submersibles

designed to
handle the immense pressures of deep
ocean waters.












The Vast World Ocean: Review

Oceanographers studying the topography
of the ocean floor have divided it into
three major zones



Continental margins


The ocean basin floor


The mid ocean ridge



The zone of transition between a
continent and the adjacent ocean basin
floor is known as the
continental
margin.
In the Atlantic, thick layers of
undisturbed sediment cover the
continental margin.
This region has very
little volcanic or earthquake activity.















The Vast World Ocean: Review


In the Pacific Ocean, where plate
boundaries converge, oceanic crust is
plunging beneath continental crust in a
subduction zone.
This force results in a
narrow continental margin that
experiences both volcanic activity and
earthquakes.



The
continental shelf
is the gently
sloping submerged area extending from
the shoreline.
On average, the shelf is
about
80 kilometers wide 130 meters
deep

at it’s seaward edge.



Continental shelves contain important
mineral deposits, large reservoirs of oil
and natural gas, and huge sand and
gravel deposits.
















The Vast World Ocean: Review


Marking the seaward edge of the
continental shelf is the
continental
slope.

The slope is steeper than the
shelf and it marks the transition from
continental crust to oceanic crust.

The
average slope is 5 degrees.



Deep, steep sided valleys known as
submarine canyons
are cut into the
continental slope.
Submarine canyons
are formed by erosion from underwater
currents.

















The Vast World Ocean: Review


In regions where trenches do not exist,
the steep continental slope merges into
a more gradual incline known as the
continental rise
.
Here the steepness of
the slope drops to about 6 meters per
kilometer.
Where the width of the
continental slope averages only about
20 kilometers wide, the continental rise
may be
hundreds of kilometers wide
.



Deep ocean trenches
are long, narrow
creases in the ocean floor that form
the deepest parts of the ocean.
Most
trenches are located along the margins
of the Pacific Ocean, and many exceed
10,000 meters (almost 30,000 feet) in
depth.



















Continental rise

The Vast World Ocean: Review


Between the continental margin and
mid
-
ocean ridge, lies the
oceanic basin
floor.

The size of this region is
comparably equal to the percentage of
land above sea level.




This region includes deep ocean
trenches, very flat areas known as
abyssal

plains
, and tall volcanic peaks
called
seamounts

and
guyots
.



Abyssal plains
have accumulations of
thick accumulations of fine sediment
that have buried an otherwise rugged
sea floor.




















_______

The Vast World Ocean: Review


The submerged volcanic peaks that dot
the ocean floor are called
seamounts
.
They are volcanoes that have not
reached the ocean surface.



Once underwater volcanoes reach the
surface, they form islands.
Over time,
running water and wave action
erode
these islands to near sea
-
level.
Over
millions of years, these islands
gradually sink below sea
-
level.
These
once active flat
-
topped but now
submerged structures are called
guyots.
























The Vast World Ocean: Review


The
mid
-
ocean ridge
is located near the
center of most ocean basins.
The
mid
-
ocean ridge system
is an
interconnected system of underwater
mountains that have developed on newly
formed ocean crust.
This system is the
longest topographic feature on Earth
running 70,000 kilometers around the
world’s oceans.



A high amount of volcanic activity takes
place along mid
-
ocean ridges.
This
activity is associated with
sea
-
floor
spreading
.
Sea
-
floor spreading occurs
where divergent plate boundaries are
moving apart from each other.
New
ocean is formed at mid
-
ocean ridges as
magma rises between diverging plates
and cools.

























The Vast World Ocean: Review


Except for steep areas of the
continental slope and the crest of the
mid
-
ocean ridge, most of the sea floor
is covered with
sediment
.
Some of this
sediment has been deposited by
turbidity currents
.
The rest has slowly
settled to the seafloor from above.



The thickness of ocean seafloor
sediments varies.
Some
trenches

act as
traps of sediment originating on the
continental margin.
The accumulation of
sediment may approach as much as 10
kilometers in thickness.
In general
accumulations of sediment are much
less, about 500 to 1000 meters.


























The Vast World Ocean: Review


Ocean floor sediments can be
classified, according to their
origin, into
three broad categories
:


Terrigenous sediments


Biogenous sediments


Hydrogenous sediments



Terrigenous sediment
is sediment
that originates on land.


Biogenous sediment
is sediment
that is biological in origin.
Biogenous sediments consist of
shells and skeletons of small
marine animals and algae.


Hydrogenous sediment
consists of
minerals that crystallize directly
from the ocean water through
various chemical reactions.





























Ocean bottom sediment map.
Lithogenous

areas are mauve,
biogenous areas
are purple and
brown (purple = siliceous ooze,
brown = calcareous ooze), and
hydrogenous areas are blue.

The Vast World Ocean: Review


The ocean floor is rich in mineral
and energy resources.
Recovering
them however often involves
technological challenges and high
costs.
Most of the value of
nonliving resources in the ocean
comes from energy products;
oil
and natural gas.



The ancient remains of microscopic
organisms are the source of
today’s deposits of
oil and natural
gas.
These organisms were buried
in marine sediments
before

they
could decompose.

After millions of
years of exposure to heat and
pressure, the remains have
transformed into
oil and natural
gas.































The Vast World Ocean: Review


Gas hydrates
are compact chemical
structures made of water and
natural gas.
The most common type
of natural gas is
methane
, which
produces methane hydrate.
Gas
hydrates occur beneath
permafrost areas on land and
under the ocean floor at depths
below 525 meters.



Most oceanic
gas hydrates
are
created when bacteria break down
organic matter trapped in ocean
-
floor sediments.
Gas hydrates
resemble chunks of ice but ignite
when lit by a flame.
The hydrates
burn because methane and other
flammable gases are released as
the gas hydrates evaporate.

































The Vast World Ocean: Review



The offshore
sand and gravel
industry is
second in economic value only to the
petroleum industry.




Sand and gravel
, which include rock
fragments that are washed out to sea and
shells of marine organisms, are mined by
offshore barges using suction devices.



Sand and gravel are used for landfill, to
fill in recreational beaches, and to make
concrete.

































The Vast World Ocean: Review


As described earlier,
manganese nodules
are hard lumps of manganese and other
metals that precipitate around a small
object. They are found in fields in deep
ocean areas.
They contain high
concentrations of manganese, iron, and
smaller concentrations of copper, nickel,
and cobalt.



These alloys are used in high
-
speed
cutting tools, powerful permanent
magnets, and jet engine parts.
With
current technology, mining of the deep
-
ocean floor for deposits of manganese
nodules is
possible

but
not

economically
profitable.




































The Vast World Ocean: Review

Evaporative salts
:



When seawater evaporates, the
salts increase in concentration
until they can no longer remain
dissolved.



When the concentration becomes
high enough, the salts
precipitate out of solution and
form halite (salt) deposits.



These halite deposits can than
be harvested.
At right is the
process from the website of a
commercial sea
-
salt greenhouse
system in Marshfield Maine.




































How We Extract Natural Sea Salt from Ocean
Water

1.
Our solar greenhouses, known as "salt houses"
are filled with fresh sea water from the Gulf of
Maine.


2.

The sea water evaporates naturally, from the
heat of the sun and the drying effects of the wind
blowing through the greenhouses.


3.

Over a period of time, fleur de
sel

floats on the
pool surface, then grows and sinks to the floor to
form the salt bed.


4.

When all of the water has evaporated, the sea
salt is ready to be packaged as natural Maine Sea
Salt™, seasoned with our natural ingredients, or
smoked over a wood fire.